The direct use of carbon in a fuel cell to generate electricity is an attractive approach for power generation. A number of carbonate and alkali fuel cells have been used for the direct generation of electricity from treated coal (i.e., ultra low sulfur/ash coal).
Conventional solid-oxide fuel cells utilize an electrolyte located between an anode and cathode facilitating the transfer of ions there between. Traditionally solid-state fossil fuels, such as coal, had to be gasified and reformed prior to being introduced to a solid-oxide fuel cell to generate electric energy. Although additional processing steps are required, the use of such solid-state fossil fuels to generate electricity remains an attractive option due in part to the high energy density of such fuels. The separate gasification and reforming steps requiring a substantial influx of thermal energy, and with heat recovery being low, an inefficient process results.
The basic principles of carbon-based fuel cells are well known in the art. Carbon (i.e., C) fuel is supplied to the anode side of a fuel cell while air is provided to the cathode side. Oxygen from the air adsorbs on the cathode catalyst. Depending on the type of electrolyte used, oxygen is converted to O2−, OH− or CO32− with H2O or CO2, according to the corresponding the cathode reaction category, discussed later in Table 1. In an alkali fuel cell, O2− reacts with H2O to form OH− on the cathode catalyst. OH− diffuses across liquid alkali membrane to the anode in order to react with carbon to produce CO2 and electrons. In a carbonate fuel cell, O2− reacts with CO2 to form carbonate on the cathode catalyst. Carbonate serving as electrolyte can further react with carbon to produce CO2 and electrons on the anode catalyst. These fuel cells operate at 400 to 650° C. The major shortcoming of these fuel cells being their short life span when using coal as the fuel. This is resulted from the build up of flyash and a poisoning of electrodes by sulfur compounds in coals. The long period of operation for these fuel cells can only be achieved by using high purity carbon as the fuel.
The use of high temperature solid oxide electrolytes and perovskite catalysts allows for conversion of oxygen to O2− which diffuses across the electrolyte membrane to the anode for oxidation. Methods employing other solid oxide membranes use liquid anodes to carry out the oxidation of carbon to carbon dioxide and are known in the art. One issue with the liquid anode approach is that such an approach faces the challenge of rapid deactivation. A recent approach utilized a solid oxide membrane and proposed the use of fluidized bed mode of a solid oxide fuel cell technology for the direct electrochemical oxidation of coal. This proposed technology involves use of an Hg lead, of which the environmental impact is unclear.
The disclosure of WO2006/028502 details the use of Pt, Cu, Re and Ni as suitable anode catalysts for the electrochemical oxidation of solid carbon-containing fuels. There is currently a need in the art for anode catalysts being active for the electrochemical oxidation of carbon containing fuel such as coal and biomass to produce electricity and CO2 in a solid oxide fuel cell. These carbon containing fuels including but not limited to coal, coke, pretreated de-ash coal, petroleum coke, plastics, rubber, and biomass.